550 ACCOUNT OF A REPETITION OF SEVERAL OF DR SAMUEL BROWN'S 



In our earlier experiments, we supposed we had erred in not heating the cya- 

 nide sufficiently. But we were not able, by any alteration in the mode of heating, 

 to procure a substance more resembling silicon than the one we have described. 



"We have now cause to regret that we did not analyse the insoluble residue of 

 these processes more carefully. It was only cursorily examined at the time of 

 our meeting with it, as we were led to suppose it not silica, from its softness and 

 want of grittiness. But we have since had frequent occasion to notice that silica, 

 obtained from its native compounds, may be quite destitute of this property. The 

 body in question was not any compound of lead, for hydrosulphuret of ammonia 

 did not blacken it : it was quite insoluble in aqua regia : bore the full blast of 

 the blowpipe without diminution in bulk ; and fused with carbonate of soda into 

 a globule of a greyish colour. On the whole, it seems to us in the highest degree 

 probable that it was silica, but we cannot confidently affirm that it was. 



The compound, or mixture of cyanide and chloride of lead, already referred 

 to, which did not fuse, yielded on heating, a bluish-grey powder, which dissolved 

 entirely in very dilute nitric acid, without the separation of any brown powder. 

 When the lead was precipitated by muriatic acid, the chloride removed by filtra- 

 tion, the liquid evaporated to dryness, and the residue plentifully washed with 

 boiling water, a trace of silica remained. The fusible precipitate was not subjected 

 to a particular examination. 



Disappointed in the cyanide of lead, we turned our attention to the similar 

 salts of other metals ; for it is within the scope of Dr BBOWN'S hypothesis, that 

 every cyanide which can be converted into a paracyanide, may have its carbon 

 transmuted into silicon. 



We rejected, after several trials, the cyanides of zinc and copper, and turned 

 our attention to one of the best known of all the compounds of this class, the cya- 

 nide of silver. This salt has the great advantage of being quite stable, and easily 

 prepared pure in any quantity. But, on the other hand, it gives off cyanogen at 

 so low a temperature, that it cannot be entirely converted into paracyanide by 

 heat in open tubes ; and the variable proportion of metallic silver which is thus 

 mingled with the product, entirely unfits it for yielding quantitative results. By 

 adopting a suggestion of Dr BROWN'S, however, and heating the cyanide in glass 

 tubes sealed at both ends, or in brass tubes closed by screw stoppers, we prevented 

 the evolution of cyanogen, which otherwise would have occurred. 



Pure dry cyanide of silver heated under pressure in this way over a gas 

 flame, slowly changed into a brown powder, which, if the heat were not raised too 

 high, did not fuse or adhere to the glass. This powder, according to Dr BEOWN'S 

 views, is either a combination of two atoms of silver, and one of paracyanogen, a 

 sub or diparacyanide of silver, or a mixture of silver and paracyanogen, in these 

 proportions. 



Where glass was used, when the tube was filed across, a slight explosion and 



